1. Field of the Invention
A cleaning system to remove soluble hydrocarbon residue and other contaminants from essentially nonporous objects or surfaces.
2. Description of the Prior Art
Various vapor generating apparatus have been designed to clean barges, tanker ships, rail tank cars, refineries and storage tank farms. Increasingly stringent worker safety and waste disposal regulations have created an environment in which alternative methods of large-scale cleaning of hydrocarbon residues and hazardous wastes are dictated and essential.
Presently, the predominant cleaning method employs the use of high pressure water systems. Such systems require workers to physically enter tanks containing hazardous residues. Because of the danger to workers, OSHA has strengthened regulations relating to confined entry (Occupational Safety and Health Standards, Part 1910, Subsection 146). These regulations now require such costly safety equipment and procedures that the market is eagerly searching for ways to adopt new cleaning systems which minimize or eliminate the need for workers to enter tanks.
Moreover, the large volume of water and waste material generated by these high water pressure water systems must be handled and processed. Because of past abuses, new EPA regulations sharply limit or control the disposal of the waste material by such cleaning systems.
U.S. Pat. No. 4,332,626 describes a process for removal of oxidizable liquid organic chemical residue from large vessels by a non-catalytic method comprising heating the vessel by introducing a heat source and oxygen into the interior of the vessel wherein the emitted heat volatizes substantially all and decomposes at least a portion of the oxidizable liquid organic chemical contaminating the interior of the vessel. The vessel combustion gas resulting from the volatilization and decomposition of the liquid organic chemical is fed from the vessel, filtered and vented to the atmosphere combustion gas essentially free of the particulates and oxidizable organic chemical.
U.S. Pat. No. 3,046,163 shows a method of cleaning the interior of a tank holding oil, grease, crude petroleum products, coal tar products, resinous products, paints or plasticizers comprising the steps of first passing hot vapor of a chlorinated hydrocarbon solvent into the tank and condensing the vapor on the tank walls dissolving adhering dissolvable matter on the interior surfaces of the tank and loosening clinging solid deposits; draining off the contaminated condensation formed and recovering the solvent; pressure spraying the interior of the tank with chlorinated hydrocarbon solvent in liquid form to remove the clinging matter loosened during the first step, draining the sludge formed from the tank and recovering the solvent from the sludge; passing hot chlorinated hydrocarbon solvent vapor into the tank, and passing unheated outside air through the tank to purge it of solvent odors and recovering the remaining traces of solvent vapor from the air before releasing the air into the atmosphere.
U.S. Pat. No. 2,348,465 teaches a process for removing grease and oil from the surfaces comprising the steps of diminishing the pressure in a closed space adjacent a surface to be cleaned, admitting the vapor of a solvent and condensing the solvent vapor on the surface, the vapor being admitted under pressure to increase the speed of condensation; cooling the surface to further increase the speed of the process; drawing off the condensed solvent and continuing the operation until nearly clean solvent drains off; shutting off the influx of vapor and extracting the last remainders of condensed solvent by diminishing the pressure to produce a high degree of vacuum and evaporating the remaining solvent and sucking off the vapor created by such final flashing-out, and applying heat to increase the speed of the evaporation and the removal.
U.S. Re. 20,976 describes a generator for use with a steam coil or other source of heat for vaporizing the solvents for cleaning surfaces within a tank comprising heating an oil solvent to form a vapor under pressure, delivering the solvent vapor into the tank displacing a horizontal layer of the air at the top of the tank while leaving the body of air in the tank below the solvent vapor as a means for retarding the speed of descent of the vapor, continuing the initial delivery of the solvent vapor to build up pressure within the tank, and after an interval sufficient to permit the air to rise to the top portion of the tank above the descended heavier solvent vapor, discharging the air from the tank by relieving the pressure.
U.S. Pat. No. 5,017,240 teaches a method for the removal and recovery of hydrocarbons which are contained within the air/vapor mixture in bulk oil or gasoline storage tanks using fractional condensation with cryogenic cooling.
Additional examples of the prior art are found in U.S. Pat. Nos. 2,324,804; 4,696,073 and U.S. Pat. No. 5,041,165.
Unfortunately the prior art exhibits the various danger or drawbacks to both workers and the environment as well as limited effectiveness of the cleaning process.
In contrast, the present invention requires no entry by workers into tanks, substantially reduces the volume of waste removed from tanks, significantly reduces cleaning time and allows cleaning in a wide range of climates including sub-freezing weather.